As wireless technologies proliferate, mobile wireless devices incorporate a multiplicity of different wireless standards. For example, a cellular telephone can accommodate a cellular network (e.g., Universal Mobile Telecommunications System), a wireless local area network (“WLAN”), such as IEEE 802.11, and a wireless personal area network (“WPAN”), such as Bluetooth (BT). Including WPAN access makes utilization of a wireless device more convenient by allowing use of wireless headsets and other short-range wireless appliances.
Mobile wireless devices are sometimes capable of accessing multiple wireless networks. Some wireless networks occupy an adjacent or overlapping frequency spectrum. For example, BT and IEEE 802.11b/g/n (for WLAN) both utilize the same 2.4-2.5 GHz band. Access to such overlapping networks can be coordinated via time multiplexing or frequency multiplexing to reduce performance degradation caused by collisions that may occur when these networks are simultaneously accessed. However, such multiplexing is often at the cost of shorter medium time available to each radio and thus lower performance, as a radio may be blocked from transmitting or receiving packets temporally to avoid collisions.
The limited medium time available to each radio is more problematic when a single mobile wireless device such as a cellular smart phone supports both radios in overlapping RF bands (referred to herein as a “combo device” short for combination device). For example, a wireless device that supports both WLAN Access Point (AP) functionalities with simultaneous BT activities.
Collisions may occur in a wireless communication medium when multiple stations (STAs) within an RF transmission coverage area concurrently utilize overlapping RF channels. RF channels may overlap when at least one frequency is common between two or more of the concurrent RF channels. Collisions may result in unsuccessful transfer of data via the wireless communication medium, which may in turn result in reduced data transfer rates for data transmitted by the STAs. For example, a user may use his or her cell phone as a WLAN AP so that he or she can share, show, print, and synchronize content by connecting with other Wi-Fi consumer electronics (CE), such as a digital picture frame, without an infrastructure network nearby. At the same time, the user may listen to stereo music played by the cell phone via a BT headset.
In one particular arrangement, a cell phone displays photos to a digital picture frame through Wi-Fi, serving as a WLAN AP. At the same time, the cell phone can play music through a BT headset. Conventional collision protection techniques such as powersave (PS) and CTS-2-Self are not applicable or are inefficient in avoiding rate or packet drops between the cell phone and the digital picture frame.
For example, FIG. 1 depicts an example timing diagram for a known combo device (e.g., cell phone) comprising a first and a second transceiver serving as a WLAN AP showing WLAN signals received over a first network from a WLAN STA by the first transceiver and Advanced Audio Distribution Profile (A2DP) signals transmitted by the combo device by the second transceiver over a second network to a WPAN device such as a BT device. The wide line on the time axes indicate the time intervals that the first and second transceivers are granted access to the medium (e.g., by a processor on the combo device). As the combo device is serving as a WLAN AP is assumed to be always on, the PS mode for the combo device is not available, so packets over the first network can arrive any time from a STA associated to the combo device, even when BT is granted and is occupying the medium.
It can be seen in FIG. 1 that BT transmission activities by the combo device are handled in a batch-mode with the three (3) A2DP packets shown transmitted one right after the other (back-to-back-packets). When the WLAN STA misses the CTS frame shown (e.g., due to being in PS mode) transmitted by the combo device, the WLAN STA transmits initial packets shown received at the combo device as RX1, and the WLAN STA starts retransmitting including retransmissions of the same packets to the combo device shown as RX2-4 during the combo node's BT activities (where BT is granted access to the medium). This is because when the STA sends a packet to the combo device, the STA expects an acknowledgment (ACK) from the combo device following the transmission. If the ACK has not been received in time, the STA will retransmit the same packets up to some predetermined limit of attempts/times. Such retransmissions reduce the PHY rate which reflects the speed at which client devices communicate with the combo device/AP, and can also lead to packet drops if no ACK is received by the STA when the retransmission number limit is reached.
Thus, when a combo device serves as a WLAN AP with concurrent coexisting overlapping network traffic, such as BT A2DP and IEEE 802.11b/g/n WLAN traffic, the conventional protection technique of CTS is undesired or even ineffective, such as when an associated STA is in PS mode. If a STA starts transmitting during the combo device's BT activities, continuous retransmissions can lead to a reduced PHY rate or even packet drops as shown in FIG. 1, which will significantly lower the network throughput. In addition, the CTS frames will block the nearby networks from communicating during the combo node's BT activities, which can significantly reduce channel utilization in nearby networks.